Depends. They've really been whoring out the series as of late with PSP, Two PS3 titles, etc. It's a wonderful series that needs time in the oven to flourish and not to be over exposed necessarily.
It's also a series that will get tremendously better with increasing technology dumped into it. The physics, the gadgets, the level size and creation aspects as well.
Which is why I believe, one full-fledged LBP game a generation would be absolutely ideal, with expansion (Level, creation, character) packs released throughout the generation. Similar to Mario and it's trajectory. Possibly with a future outlook of diversifying the series from 2D / 3D. But always keeping the scope the original game had.